<h1 id="washington-congressional-districts">2020 Washington
Congressional Districts</h1>
<h2 id="redistricting-requirements">Redistricting requirements</h2>
<p>In Washington, districts must, under <a
href="https://leg.wa.gov/CodeReviser/Pages/WAConstitution.aspx">Article
2, Section 43 of the constitution</a> and <a
href="https://apps.leg.wa.gov/RCW/default.aspx?cite=44.05.090">RCW
44.05.090</a>:</p>
<ol type="1">
<li>be contiguous</li>
<li>have equal populations</li>
<li>be geographically compact</li>
<li>preserve county and municipality boundaries as much as possible</li>
<li>not be connected across geographic barriers, although ferries across
water may establish contiguity</li>
<li>“provide fair and effective representation and … encourage electoral
competition”</li>
</ol>
<h3 id="algorithmic-constraints">Algorithmic Constraints</h3>
<p>We enforce a maximum population deviation of 0.5%. We apply a
county/municipality constraint, as described below. To reflect the
barriers and contiguity requirements, we remove edges across water
regions and mountains in the adjacency graph, but reconnect precincts
which are linked by a bridge, highway, or ferry.</p>
<h2 id="data-sources">Data Sources</h2>
<p>Data for Washington comes from the ALARM Project’s <a
href="https://alarm-redist.github.io/posts/2021-08-10-census-2020/">2020
Redistricting Data Files</a>.</p>
<h2 id="pre-processing-notes">Pre-processing Notes</h2>
<p>As described above, the adjacency graph was modified by hand to
reflect Washington’s contiguity requirements. The full list of these
changes can be found in the <code>01_prep_WA_cd_2020.R</code> file.</p>
<h2 id="simulation-notes">Simulation Notes</h2>
<p>We sample 16,000 districting plans for Washington across two runs of
the SMC algorithm, then filter down to 5,000 total plans. To balance
county and municipality splits, we create pseudocounties for use in the
county constraint. These are counties, outside of King County, Pierce
County, and Snohomish County. Within King County, Pierce County, and
Snohomish County, each municipality is its own pseudocounty as well.
King County, Pierce County, and Snohomish County were chosen since they
are necessarily split by congressional districts. To comply with the
federal VRA and to respect communities of interest, we add a weak VRA
constraint targeting one majority-minority district (currently
WA-09).</p>
<h2 id="contents">Contents</h2>
<ul>
<li><code>WA_cd_2020_stats.csv</code> contains summary statistics on the
sampled redistricting plans</li>
<li><code>WA_cd_2020_plans.rds</code> is a compressed
<code>redist_plans</code> object, which contains the matrix of
precinct/block assignments and may be used for further analysis.</li>
<li><code>WA_cd_2020_map.rds</code> is a compressed
<code>redist_map</code> object, which contains the precinct/block
shapefile and demographic data.</li>
</ul>
<p>Both the <code>redist_plans</code> and <code>redist_map</code> object
are intended to be used with the <a
href="https://alarm-redist.github.io/redist/">redist package</a>.</p>
<h3 id="codebook-for-summary-statistics">Codebook for summary
statistics</h3>
<ul>
<li><code>draw</code>: unique identifier for each sample. Non-numeric
draw names are real-world plans, e.g., <code>cd_2010</code> for an
enacted 2010 plan.</li>
<li><code>district</code>: a district identifier. District numbers
roughly match those in the enacted plan, but the correspondence is not
perfect.</li>
<li><code>chain</code>: a number identifying the run of the
redistricting algorithm used to produce this draw. Used for diagnostic
purposes.</li>
<li><code>pop_overlap</code>: a number indicating the fraction of people
in this plan who reside in the same-numbered district in the enacted
plan.</li>
<li><code>total_pop</code>: the total population of each district.</li>
<li><code>total_vap</code>: the total voting-aged population of each
district.</li>
<li><code>pop_*</code>, <code>vap_*</code>: total (voting-aged)
population within racial and ethnic groups for each district. Variable
codes documented <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>plan_dev</code>: the maximum population deviation among
districts in the plan. Computed as
<code>max(abs(distr_pop - target_pop)/target_pop)</code>.</li>
<li><code>comp_edge</code>: compactness, as measured by the fraction of
internal edges kept. Higher values indicate more compactness.</li>
<li><code>comp_polsby</code>: compactness, as measured by the
Polsby-Popper score. Higher values indicate more compactness.</li>
<li><code>county_splits</code>: the number of counties which belong to
more than one district.</li>
<li><code>muni_splits</code>: the number of Census Designated Places
which belong to more than one district.</li>
<li><code>*_##_dem_*</code>, <code>*_##_rep_*</code>: vote counts for
statewide Democratic and Republican candidates in a certain election.
More information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>adv_##</code>, <code>arv_##</code>: average vote counts for
statewide Democratic and Republican candidates in a certain year. More
information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>ndv</code>, <code>nrv</code>: averages of the
<code>adv_##</code> and <code>arv_##</code> variables across all
available elections.</li>
<li><code>ndshare</code>: normal Democratic share, computed as
<code>ndv / (ndv + nrv)</code></li>
<li><code>e_dvs</code>: average Democratic vote share, computed as the
average of the Democratic vote share when first scored under each
statewide election.</li>
<li><code>pr_dem</code>: probability seat is represented by a Democrat;
calculated as the fraction of statewide elections under which the
district had a majority Democratic share.</li>
<li><code>e_dem</code>: expected number of Democratic seats for the
plan; equivalent to summing the <code>pr_dem</code> values across
districts</li>
<li><code>pbias</code>: partisan bias at 50% vote share, averaged across
all available elections. Positive values indicate Republican bias.</li>
<li><code>egap</code>: the efficiency gap, averaged across all available
elections. Positive values indicate Republican bias.</li>
</ul>
